1. Field of the Invention
The present invention relates to a wet type multi-plate friction engaging apparatus used in an automatic transmission of a vehicle and the like. More particularly, the present invention relates to a wet type multi-plate friction engaging apparatus including means for preventing a relative rotation between a clutch housing and a piston.
2. Related Background Art
In a wet type multi-plate friction engaging apparatus, a power is transmitted by engaging a plurality of friction engaging elements disposed within a clutch housing with each other. In order to apply an axial urging force to the friction engaging elements, a piston shiftable in an axial direction is provided within the clutch housing.
The piston is shifted in the axial direction by supplying oil pressure into an oil pressure chamber defined between the piston and the clutch housing, thereby tightening or engaging the friction engaging elements. In order to maintain the oil pressure chamber in a liquid-tight condition, an O-ring is provided on an outer periphery of the piston.
When the piston of the wet type multi-plate clutch is operated, the piston for tightening the friction engaging elements may be rotated by the rotation of the friction engaging elements. If the piston is rotated upon engaging the friction engaging elements, due to the rotation of the piston, the O-ring arranged around the piston may be damaged. Further, due to the rotation of the piston, a spring connected to the piston may be twisted to damage the spring. As a result, peripheral members may be damaged, thereby causing mal-function of the clutch.
In order to solve such problems, for example, in Japanese Utility Model Application Laid-open No. S50-101747 (1975), a drive plate or friction engaging element adjacent to a piston is provided with a pawl portion extending in an axial direction so that, by engaging the pawl portion with a groove or a hole formed in the piston, a relative rotation between a clutch housing and the piston is prevented.
Further, in Japanese Utility Model Application Laid-open No. S50-94345 (1975), by fitting a stop member attached to an outer periphery of a piston into a spline formed in a clutch housing, a relative rotation between the clutch housing and the piston is prevented.
However, as shown in the above-mentioned. Japanese Utility Model Application Laid-open No. S50-101747, if the pawl portion is provided on the drive plate, the pawl portion abuts against the groove of the piston repeatedly for preventing the relative rotation, with the result that the drive plate may be deformed due to impact or shock. If such deformation occurs, a normal or correct function of the friction engaging apparatus will be lost.
On the other hand, the above-mentioned Japanese Utility Model Application Laid-open No. S50-94345 causes a problem that the number of parts is increased because an additional member as the stop member is provided on the piston.
Further, in the above-mentioned Japanese Utility Model Application Laid-open No. S50-101747 and Japanese Utility Model Application Laid-open No. S50-94345, since the relative rotation is prevented by directly engaging the piston with the clutch housing, the relative rotation may not be prevented satisfactorily.